Applicants' invention relates to electrical enclosures of the explosion-proof type normally used in environments which may contain explosive mixtures of gases or dust. Applicant is aware of U.S. Pat. Nos. 3,317,072; 3,573,343; 3,582,535; 3,585,273; 3,724,706; 3,853,291; and 3,974,933, the disclosures of which are incorporated by reference herein.
The present invention relates to an enclosure, such as a cast box, in particular to an enclosure that is of the type that is especially useful as an explosion-proof receptacle for electrical apparatus that is subject to sparking. The present enclosure is preferably cast and consists of two principal parts, a box or enclosure vessel and a cover. Each of the parts is unitary in itself, being formed of a single piece of metal. The box portion may be formed with access holes which may be threaded, joined to conduit, and sealed to make a complete explosion tight path for electrical wiring, as is known in the art.
The present box is preferably made of cast aluminum and has a design such that the bolt holes are either formed in the process of casting or milling. The holes may be tapped, but may also be formed without tapping so the self tapping screws or bolts can be used to fasten the cover onto the vessel portion.
One object of the enclosure is to prevent explosions from propagating out and spreading over a wide area of a building or the like. The enclosure is strong and rigid to contain the explosion. The construction of the enclosure, particularly with mating flanges between the box and cover, make an extremely strong apparatus. By forming the box and cover reasonably accurately, machining of the parts is minimized and a tight fit adds strength to the enclosure.
Another object of the invention is to provide a seal for the fitting of the cover onto the vessel that can be provided inexpensively, yet will afford a very tight engagement. The mating flanges of the box and cover are in close contact to restrict, cool and quench burning gases resulting from an internal explosion. The flanges aid in obtaining a tight seal and make it possible to obtain long flame paths that retard escape of the flame from the box.
By placing an elastomeric type seal between the box and cover additional advantages are obtained. First, the propagation of the explosion referred to above is better contained. Second, the seals retard entry of corrosion producing chemicals and moisture. The seal thus prevents interference with the contacts, switches, and other electrical devices contained in the enclosure. The seal may be joined by an adhesive or other conventional means and installed in the enclosure vessel or in the cover, thereby eliminating some expense.
Another object is to provide lugs for the mounting of the box upon a base or another support. These lugs can be separate from the box itself. By making the lugs separate, the casting of the box is considerably simplified. And more importantly, the lugs are designed so that they can be mounted to extend either to the sides or to the ends of the box by a very simple mounting change, requiring no more than swiveling the legs about their mounting screws.
A further object of the invention is to provide a means to relieve the bolt load on the bolts joining the cover to the enclosure, in the event that an internal explosion occurs in the box. This reduces the number of bolt holes and bolts that are required, reducing the expense in manufacturing the box, and also greatly increasing the convenience of the use of the box, since fewer bolts need be installed or removed to complete an installation of the box or to examine or work in the interior of the box after installation.
A futher object of the invention is to provide means whereby the cover is made exceptionally rigid so that it will remain in explosion-retaining contact with the enclosure vessel when subjected to an internal explosion. A further object is to provide means to maintain the explosion tight seal between the cover and the enclosure vessel, while eliminating or reducing the number of bolts or other joining means.
Another object of the invention is to provide simplified access to the interior of the enclosure. By reducing the number of bolts access is made easier and quicker since fewer bolts must be loosened. Access is provided so that the seal between the box and the cover is easily broken.
Other objects will appear from the description and drawings.